1. Field of the Invention
The present invention relates to a process for preparing temperature-responsive polymers that may be formed into a thermally-processable material which exhibits flushability properties when immersed in water such that the temperature-responsive polymer may be used in a disposable absorbent product to impart flushability properties to the product. The process prepares the temperature-responsive polymer in an aqueous solution using a chain transfer agent.
2. Description of the Related Art
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, the outer cover backsheet materials of the disposable absorbent products are typically made of liquid-insoluble and liquid impermeable materials, such as polypropylene films, that exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer and does not allow leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products can be difficult to dispose of into an aqueous environment. For example, attempts to flush many disposable absorbent products down a toilet into a sewage system typically lead to blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the outer cover materials typically used in the disposable absorbent products generally do not disintegrate or disperse when flushed down a toilet so that the disposable absorbent product cannot be disposed of in this way. If the outer cover materials are made very thin in order to reduce the overall bulk of the disposable absorbent product so as to reduce the likelihood of blockage of a toilet or a sewage pipe, then the outer cover material typically will not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by a wearer.
As such, there is a need for new materials that are relatively easy to process and may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the products may be disposed of into an aqueous environment. For example, the disposable absorbent product may be easily and efficiently disposed of by flushing the disposable absorbent product down a toilet. Such a disposable absorbent product would then be capable of being degraded by a liquid sewage system as compared to having to be disposed of into a landfill or other solid waste disposal system.
Processes known to be useful in preparing temperature-responsive polymers include free-radical solution polymerization, inverse suspension polymerization, or polymerization in organic solvents. However, such processes have generally been found to result in the temperature-responsive polymer being substantially crosslinked and/or exhibiting an intrinsic viscosity that is too high so as to prevent the temperature-responsive polymer from being capable of being thermally processable.
As such, there is a need for a process that is relatively easy to use and which process results in a temperature-responsive polymer that may then be thermally processed to prepare a material form that may be used in a disposable absorbent product to impart flushability properties to the product.